190 



Picea orientalisj die (|uickly. This is ascribed to winter fro^t hut u\Hm 

 closer observation it is discoxered that low temperatures become harmful 

 onl\- when the soil is very wet'. 



A dehciency of s(jil aerati(;n is the most harmful factf)r since upon the 

 aeration depend the phenomena of decay in the decomposition of organic 

 masses. Thus in judging loamy soils as to their fertility not only the de- 

 gree of friability, but also the depth to which this extends, becomes decisive. 

 Since the firm loam layers of the subsoil are aerated only with difficulty, 

 the spreading out of the root system takes place only in the friable layers. 

 Therefore a special value should be laid on the maintenance of this friabil- 

 ity. This must be taken especially into consideration in forests, where the 

 lifter is cDnstcintly raked away. Ramann's investigations- sliow that, in re- 

 moving litter, the soil becomes densely packed and works harm to the 

 forest tract. 



The packing of soil and the necessity for loosening it should especially 

 be considered in growing all tropical plants, as Vosseler^ has proved. 

 He describes the soils characterized by Koerts as "older red loam." and 

 especially the primeval forest soil of East Usambara thus; — "The red 

 soil consists mainly of fine loam and clay which is pervious but too finely 

 porous to take up small humus particles ; besides, chemical action 

 takes place possibly in the upper surfaces alone and thus prevents 

 their penetration into the lower soil. .Since the soil itself is the final pro- 

 duct of decomposition, it lacks the ad\antage of processes of loosening up 

 which i)ossibly take i)lace during such action." Mere also, therefore, the 

 loosening of the soil is given as the first re(|uirement for successful culti- 

 \ation. 



The more cla}e\- the soil is, llie more slowly the \ egetable refuse will 

 be decomposed because of the lower temperature. While in sufficiently 

 friable soils, a normal decomposition takes place, masses of raiv humus 

 collect on thick clay soils, i. e., particles of plants, which are only slightly 

 decomposable, remain deposited on the soil because the conditions are un- 

 favorable for decomposition. If very fine grained soils with a greater 

 moisture holdintj capacity, \. e., ability to retain large amounts of water 

 without iii\ing it olT in the form of (Irojjs. accjuire so much water that it 

 oNcrcomes the continuit}- of the substance particles by penetrating between 

 them, thus forcing them apart, the soil Ijecomes softer. This condition is 

 especiall\- peculiar to strong clay and red soil ; such a disinteijration occurs 

 less fre(|uentl\- in loam}- soil. 



.Such reduction of the soil is doubly dangerous, if it takes place in the 

 autumn or s])ring. On the one hand, the soil washes away at once and the 

 seeds are soon exposed to drying or to freezing as the case may be. On the 



1 Cordcs, VV., IlfitniH: zuni X't-ihalten der Conift're]! f^egt-n Witt I'luns.^^einflu.s.sc. 

 H;im))ur,a: U'97. 



- Ramunn, 10., rntoisiicViiing' .streiiberecliter ISi'iden. Sond. Z. f. P'oist- 11. .lagd- 

 wesen, XXX .Jahrg-; cit. Hot. .Jahresb. 1900, II. p. 4iri. 



•' Vosseler, Ueber einige Eisentumlichkeiten der I'rwaldl^i'idon O.slusambaias. 

 Mitteil. a. d. Biol. I-,andwirtsch. Institut Amani, 1904. No. 33. 



